The broad objective of this project is to contribute towards the elucidation of the biochemistry and physiology of the beta cells of the islets of Langerhans. This includes an understanding of the ways in which their structure and metabolism are geared to the synthesis and secretion of insulin and the mechanisms by which their activity is modulated by external factors. We have been using the toadfish in our studies since in this species, in contrast to mammals, the islet of Langerhans is segregated into a discrete mass which is separated from the pancreatic acinar tissue. We are studying the characteristics of the sugar transport system we have shown to be present, the metabolic pathways by which glucose is utilized, and the mechanism by which glucose and metabolic intermediates trigger insulin secretion from islet cells in vitro and from isolated insulin secretion granules. In this connection, the chemistry of the insulin secretion granule membrane, with particular reference to the role of sulfhydryl (SH) groups in insulin release, is also being examined. Our study of the mechanism of the diabetogenic action of alloxan is another approach to achieving the overall objective; understanding the basis of the selectivity of alloxan for the beta cells could provide significant information on the unique properties of these cells which enable them to carry out their specific functions. We have shown that alloxan increases the permeability of islet tissue in vitro; our evidence indicates that it does so by reacting with essential SH groups at the sugar transport site in the beta cell membrane, and that its selectivity for the beta cells arises, at least partly, from differences in the SH groups in different cell membranes. Therefore we are comparing, in islet and other tissues, the reactivity of these groups with SH-binding reagents under different conditions, and testing the ability of various thiols and sugars to protect against and reverse the action of these reagents; we are also attempting to isolate the cell membrane unit with which alloxan reacts in order to characterize it directly. By means of these and other studies we hope to establish the exact mechanism of the selective destruction of the beta cells by alloxan.